Worn PW3 cam

Knowing DNC and who else he makes cams for, this sounds like a batch issue - the PW3 has been around a long time. With the current steel supply in overdrive and long delays in delivery, there is an awful lot of remelt being used at the moment of dubiuos quality. There must be some owners out there doing big mileages, what do they have fitted.

Part of the problem could be the Comstock conical springs. They have more pressure over the nose compared to other springs set up for street. More pressure = more wear. Figures below are for recommended installation height (each is different).

oldmikew asked about EN40B steel.
I have used Newman cams made of EN40B steel with special Plasma nitriding (more expensive) and no problems.

Click to expand...

Thanks for posting on Newman cams... that is reassuring. Spring pressure may well contribute to cam wear and I wonder if revs are kept down to say 7,500 whether there is any need for such high pressures to prevent valve float but then that presumably would also depend on the cam profile.

Knowing DNC and who else he makes cams for, this sounds like a batch issue - the PW3 has been around a long time. With the current steel supply in overdrive and long delays in delivery, there is an awful lot of remelt being used at the moment of dubiuos quality. There must be some owners out there doing big mileages, what do they have fitted.

The nose pressures you quote are only found in a stationary engine.
The moment the engine runs, the nose pressures are reduced, and the higher the engine revs, the greated the reduction.
A correctly ground PW3 profile has no dynamic issues when used with Comstock's conical springs, but the choice and quality of the camshaft material is another matter entirely.

The moment the engine runs, the nose pressures are reduced, and the higher the engine revs, the greated the reduction.

Click to expand...

Snotzo
Is that really true?
Intuitively I would have guessed peak pressures would go up on a running engine compared to stationary.
Statically you are only dealing with the spring constant times deflection (plus gravity if you're picky)
Dynamically you still have the spring constant (+ gravity) plus inertial forces associated with accelerating the mass of the valve train.
This logic would, of course, see a lower pressure during valve closure (hence valve "float") - but higher peak pressures (during valve opening).
This, of course, ignores situations of valve springs reaching harmonic frequencies - not predictable or welcome!

Has your statement been proven empirically? Not trying to be rude - just inquisitive.
Cheers
Rob

I call mine a premature fail.......it ran one race season of 26 races in 2015, I pretty much think it was OK until the last race day, as I wasn't needing to adjust valve clearances.

Supplied by Norman White in 2014. I asked Norman at the time I found the failure ( 2 years ago) and he said he had not had reported problems of lobe wear.

It could have been associated with revving occasionally to 8K? with a momentary 8.5K! on the last race day

I worried about shortage of oil, but can't be specific on whether there was or wasn't, but I did what I could to improve oil supply to the pump.

And I fitted a Webcam! This cam runs very strong, but the motor does not rev as much as it did. I think on lap times it is probably about even with the PW3. I need to dyno it.

However, I think the PW3 profile suited me and my motor/exhaust a little more, so if there was a hard welded one available that ran flat followers I might refit one for the profile, and adopt a lower rev limit.

I call mine a premature fail.......it ran one race season of 26 races in 2015, I pretty much think it was OK until the last race day, as I wasn't needing to adjust valve clearances.

Supplied by Norman White in 2014. I asked Norman at the time I found the failure ( 2 years ago) and he said he had not had reported problems of lobe wear.

It could have been associated with revving occasionally to 8K? with a momentary 8.5K! on the last race day

I worried about shortage of oil, but can't be specific on whether there was or wasn't, but I did what I could to improve oil supply to the pump.

And I fitted a Webcam! This cam runs very strong, but the motor does not rev as much as it did. I think on lap times it is probably about even with the PW3. I need to dyno it.

However, I think the PW3 profile suited me and my motor/exhaust a little more, so if there was a hard welded one available that ran flat followers I might refit one for the profile, and adopt a lower rev limit.

I don't want another chilled iron one.

Click to expand...

Dunstall used to offer a so called pressure feed kit for use with his racing cams- they had a very narrow nose. It bled oil through the original Atlas early commando crankcase breather and presumably exited through the breather holes halfway along the cam.. This would at least ensure there was oil getting splashed about whether it penetrates to where it is needed ,or just cavitates on the bottom of the camshaft tunnel is another matter.

I suspect thenotion is ex Jim Boughen , and he built a number of engines -not just for Dunstall but also for Gus Khun , so maybe some one somewhere
has one and could point to the approximate size of the restrictor jet

I am NOT buying your assessment of this. 10 -15 lbs added spring pressure should have NO effect on wear IF it was a properly made ie material and hardened camshaft along with a using the proper oil and break in.

Part of the problem could be the Comstock conical springs. They have more pressure over the nose compared to other springs set up for street. More pressure = more wear. Figures below are for recommended installation height (each is different).

I am NOT buying your assessment of this. 10 -15 lbs added spring pressure should have NO effect on wear IF it was a properly made ie material and hardened camshaft along with a using the proper oil and break in.

Click to expand...

Actually, the added pressure over the nose helps improve the cam life. Cams fail from loss of valve train control and pressure over the nose helps maintain control.
Of course lubrication has an impact.
Chilled iron cams have a spotty track record and any cam with high ramp rates is going to push things to the limit as far as durability. Jim

like i said i was not buying his thinking. in the automotive world 240 on the nose is not that high on flat tappet cam. a friend has a big inch drag motor with a roller cam and it is scary numbers. 1.080 lift 1,400 lbs open pressure on a 2.620 intake valve. and yes these numbers are correct

like i said i was not buying his thinking. in the automotive world 240 on the nose is not that high on flat tappet cam. a friend has a big inch drag motor with a roller cam and it is scary numbers. 1.080 lift 1,400 lbs open pressure on a 2.620 intake valve. and yes these numbers are correct

Click to expand...

No doubt, but a lot of that pressure is used to hold the valve closed against 100 psi of blower pressure....

So for Fullauto with his low Rev requirement, highly enforced speeding rules and single carb, a standard lift cam and standard springs would make sense in every way. More grunt and less stress.
I think Webcam has a standard profile, or very close to it.

rob ss
the poundages quoted by js were at peak lift, whereas you are talking about pressures at other lift positions.

The worst situation for camshafts and followers is at very low engine speeds, usually only a few hundred rpm. Here the oil entrainment is chronically bad, in the region of 0.04 microns thick, while Hertz stress is very high, typically 950 Mpa. At 8000 rpm the oil entrainment is drastically improved by better than a factor of 10, while the Hertz stress is almost halved.

At high rpm the inertia of the valve, retainer, collets and a portion of the upper spring coils, rocker inertia, pushrod and cam follower, leaves very little spring pressure available to bear on the surface of the cam.

So for Fullauto with his low Rev requirement, highly enforced speeding rules and single carb, a standard lift cam and standard springs would make sense in every way. More grunt and less stress.
I think Webcam has a standard profile, or very close to it.

Glen

Click to expand...

Wrong. The power characteristics of the PW3 cam are far better than the standard cam in my application from idle on up. I'll persevere with the PW3, just make sure that the new one is suitable.

rob ss
the poundages quoted by js were at peak lift, whereas you are talking about pressures at other lift positions.

The worst situation for camshafts and followers is at very low engine speeds, usually only a few hundred rpm. Here the oil entrainment is chronically bad, in the region of 0.04 microns thick, while Hertz stress is very high, typically 950 Mpa. At 8000 rpm the oil entrainment is drastically improved by better than a factor of 10, while the Hertz stress is almost halved.

At high rpm the inertia of the valve, retainer, collets and a portion of the upper spring coils, rocker inertia, pushrod and cam follower, leaves very little spring pressure available to bear on the surface of the cam.

Click to expand...

Yes, and when spring pressure overcomes the inertia of the opening valve -just after peak lift - this is when the valve comes back down to hard contact with the cam. That hard contact just after peak lift is what causes the little wear line down the center of your lifter. Jim